Accumulating evidence underscores the T-cell immune synapse (IS) as a site of intense vesicular trafficking, on which productive signaling and cell activation crucially depend. Although the T-cell antigen receptor (TCR) is known to exploit recycling to accumulate to the IS, the specific pathway that controls this process remains to be elucidated. Here we demonstrate that the small GTPase Rab29 is centrally implicated in TCR trafficking and IS assembly. Rab29 colocalized and interacted with Rab8, Rab11 and IFT20, a component of the intraflagellar transport system that regulates ciliogenesis and participates in TCR recycling in the non-ciliated T cell, as assessed by co-immunoprecipitation and immunofluorescence analysis. Rab29 depletion resulted in the inability of TCRs to undergo recycling to the IS, thereby compromizing IS assembly. Under these conditions, recycling TCRs accumulated in Rab11 + endosomes that failed to polarize to the IS due to defective Rab29-dependent recruitment of the dynein microtubule motor. Remarkably, Rab29 participates in a similar pathway in ciliated cells to promote primary cilium growth and ciliary localization of Smoothened. These results provide a function for Rab29 as a regulator of receptor recycling and identify this GTPase as a shared participant in IS and primary cilium assembly. T-cell activation is triggered by T-cell antigen receptor (TCR) engagement by MHC-bound peptide dispayed by an antigen presenting cell (APC). While a substantial proportion of the TCR has long been known to be associated with recycling endosomes, 1 it is only recently that the central function of this pool has emerged with the finding that, on assembly of the specialized interface with the APC, known as the immune synapse (IS), intracellular TCRs are delivered to this location by polarized recycling. 2 This process ensures a steady supply of TCRs at the IS to sustain signaling for T-cell activation 3 and has been co-opted by other receptors, such as the transferrin receptor (TfR) and the chemokine receptor CXCR4, 4,5 as well as membrane-bound signaling mediators, such as the kinase Lck and the adaptor LAT. 6,7 Receptor recycling is orchestrated by the small GTPases Rab4 and Rab11. 8 Cargo specificity is achieved with the assistance of specific regulators and effectors. The TCR recycling pathway has only started to be delineated with the identification of specific mediators, which include Rab35 and its GAP EPI64C 9 and the actin adaptor WASH 10 . Specific combinations of Rabs and SNAREs have been recently associated with recycling endosomes carrying either Lck, or TCRζ and LAT. 11 We have moreover identified IFT20 12 and other components of the intraflagellar transport (IFT) system, which regulates ciliary assembly and function, 13 as unexpected regulators of TCR recycling in the non-ciliated T cell. 14 Recently a Rab GTPase subfamily, which includes Rab29, Rab32 and Rab38, has been implicated in trafficking of the Salmonella-containing vacuole (SCV) in infected epithelial cells. 15,16 Rab32 and Rab38 ...